Filament for incandescent lamps and the like



' Patented Feb. 5, l92 9.'

UNITED STA TES' PATENT OFFICE.

FRAN Z SKAUPY, OF 3111311121, GERMANY, ASSIGNOR TO GENERAL ELEGTRIC COMPANY, A CORPORATION OF NEW YORK.

FOR INCANDESOENT L AMPS AND THE LIKE.

Ho Drawing. Application filed ApriI'ZO, 1925, Serial No. 24,674, and in Germany May 3, 1924.

The present invention relates to a process for improving the mechanical properties of crystalline nonmetallic substances used for filaments of incandescent lamps, space cur.- rent devices, and the like.

pressure while still another method of ac- It is an object of the invention to increase the tensile strength and plasticity of such substances.

Another object ofthe invention is to increase the size of the crystals as well as the limits'of crystal growth of such substances.

. The novel features which are believed to p known to the art involving the use of special molds, heat treatment, and gradual cooling.

Although applicable to metals such processes have been found unsuitable for the treatment of non-metallic substances which are also suitable for filaments such as thorium oxide owing to the impossibility of working such substances into filamentary form without destruction.

In accordance with the present invention the difficulties associated with the working of 'such materials are obviated by-su'rrounding them with metallic casings which may be removed at any desired stage of the working process, as hereinafter described.-

complishing the same result consists in producing a finely granular intimate mixture of the non-metallic substance, e. g. thorium oxide, with .finely divided metal such as copper, the mixture being so proportioned that the same will be sufliciently plastic for mechanical working at the temperatures chosen.

The oxide encased in the metal container produced as above described may now be drawn down toany suitable size. The tem-' erature at which the mechanical working is eflected must be considerably above room temperature and not far removed from the melting point of the non-metallic substance since it is well known that the plasticity thereof increases with a rise in temperature.

In order to induce the formation of a long continuous crystal in the oxide mass the entire structure may be subjected to a suitable heat treatment which may for example con- ,In the preferred embodiment of the inven&

tion' the diflicultly fusible oxide, e. g. thorium oxide, .is provided with such a casing by introducing the oxide in a pulverulent ormolten state intoa tube made of a suitable ductile metal, e. g. copper, nickel, or iron, although more diificultly fusible metals such as tungsten may also be used. It is also possible to produce such a casing by electro-depositing the required metal upon the exterior of the refractory oxide when the latter has been cast or agglomerated into a suitable coherent body. Another method of producing the easing is to electroplate the individual particles of the oxide with ductile metal and agglomerate these'into a coherent mass by means of sist in heating the structure to white heat or in moving the same through a plurality of zones of gradually increasing high temperature. The heatin' may also be induced by passing a current 0 suitable strength through the non-metallic body. In order to improve the crystal structure obtained the rod or wireshaped non-metallic body may be first preliminarily heated and then subjected to a certain amount of tension so as to reduce it one or two stages whereupon it may again be reheated to a high degree.

This heat treatment which is intended to induce the formation of a single crystal may be carried out either before or after the removal of the metal casin The casing is removed preferably by (f in a suitable acid or by subjecting it to the action of a gas capable of attacking the metal, such as hydrochloric acid gas.

issolving the same In the case of a metal of low fusing point the casln may I even be removed by volatilization. en the filament'has been produced by drawin down an agglomerated mixture of oxide an metal the metal may be so intimately associated with the oxide particles that the gasboundary limits will depend upon the nature and the degree of mechanical working to which the oxide is subjected as well as upon the temperature prevailing during the heat treatment and may also depend upon. the preliminary condition of fineness of the material.

The crystal modification induced by the heat. treatment is of especial advantage in incandescent lamp and vacuum tube filaments since it is then possible to use the filaments without danger of recrystallization when subjected for a long time to high temperatures.

Under certain conditions it may also be preferable to change the oxide into a single crystal modification before subjecting it to mechanical working or drawing. Even in such a case, however, it is preferable to en-,

ing providing said material with a casing of ductile metal, drawing to filamentary size,

passing a current through the drawn product of sufficient intensity to heat said product to convert it into a uni-crystal structure and removin said casing. a

2. The method for converting non-crystal- -line oxides-into a uni-crystal structure 'comprising placing said material within a tube of ductile metal, drawing to filamentary size, subjecting the drawn product to heat treatment to convert it into a uni-crystal structure and removing said tube.

3. The method for converting a non-crystalline oxide into a uni-crystal filament which comprises placing the; oxide in a casing of difiicultly fusible metal, drawing the casing and enclosed oxide down to filamentary size and thereafter heat-treating the drawn filament to induce uni-crystal growth and removing the casing.

4. The method forconverting a non-crystalline non-metallic filament into a uni-crystal, comprising encasing said filament within a casing of ductile metal, drawing the encased filament down to size, heat treating said drawn filament to induce the growth of uni-crystal structure and removing said casmg.

In witness whereof, I have hereunto set my hand this 3rd day of April, 1925.

FRANZ SKAUPY. 

